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What are the advantages and disadvantages of have the wing positioned further aft on an airplane?
I've noticed that there is some variation in the location of the wing on airliners: The Boeing 737 has its wing mounted near the midpoint of the fuselage:

while other aircraft like the CRJ or the Airbus concept plane shown below have the wing mounted further aft.

What are the advantages or disadvantages to these wing locations, and why might a designer pick one over the other.

Also related: How does the mounting location of a jet engine affect aircraft performance?

Look where the engines are. Engines are heavy. The wing is where the center of gravity requires it to be.

The wings produce not only lift, but also a pitching moment. Usually, it is destabilizing in the sense that it causes nose up of the aircraft as the aerodynamic center is in front of the cg (which causes further nose up and so on). This moment is then counteracted by the tail.

Pic: adg.stanford.edu.
As we move the wing to the aft, the stability increases and once the wing is behind the c.g, the aircraft becomes stable.

Pic: adg.stanford.edu
Although this is stable, the configuration causes a nose down moment when lift is increased. However, we also want that the aircraft be trimmed (i.e. at moment equilibrium at the desired c.g).
With single wing, this is not easy with a reasonable static margin. Another thing is that as the wing is moved aft, the c.g also shifts aft.
It is possible to have wings in the rear. In that case, it becomes necessary to add a canard for controlling at he aircraft. A good example would be the Gyroflung Speed Canard.

As already noted, the aircraft has a canard for control.
The location of the engine and wing are related. As the engines are moved aft, the c.g. shifts in that direction and the wing is moved aft to reduce the tail surface needed.

The wing does not need to be aft of CG to make the plane stable. The condition for stability is that the forward airfoil must fly at higher AoA than the rear one, but that becomes true when the wing is still slightly forward of CG. When the wing moves aft of CG, the AoA on the horizontal stabilizer becomes negative, but that is not needed for stability, though it obviously improves it.

The overall centre of lift must be coincident (in the horizontal plane) with the centre of gravity, otherwise the plane would tip over forward or backward.
Since most planes have a large wing that contributes most of the lift and a small horizontal stabilizer that only contributes a little bit, the main wing needs to be close to the centre of gravity. So the wing is mounted further aft if the centre of gravity is further aft.
Now the cargo will always have its centre of gravity near the centre of the fuselage. So if the empty aircraft has aft centre of gravity, loading it will cause larger change of the CG position and for this it needs larger horizontal stabilizer so it can provide enough balancing force.

The cargo's centre of gravity being near the centre of the fuselage is only a given if: a) the centre of the cargo hold coincides with the centre of the fuselage as a whole, b) the aircraft is loaded to capacity, c) all the cargo is the same density, and d) the cargo is properly loaded.  None of which are necessarily true.

@Sean, d is true by requirement. If it isn't, the aircraft won't fly. Each aircraft has a weight and balance specification and you must load the cargo so its centre of gravity is within the specified range.

a) cargo loaders are not always competent (judging from the number of accidents in which improperly-loaded cargo was either a contributing factor or the main probable cause), and b) if the centre of gravity isn't too far outside the limits, the aircraft will probably still be capable of flight (at least initially), albeit with a seriously degraded margin of safety and the vast majority of its pitch control authority in the direction opposing the pitching moment caused by the misloaded cargo used up in opposing said pitching moment.

This is why a sliding cargo bay floor might be better than the monstrous tail of the Hercules.  Simply mount a roller at CG.  When done loading, pull the floor forward until it tips.  Load, and plane, now balanced.

Rear placement of the wing was heavily influenced in design philosophy by the effort to develop planforms for supersonic flight, but goes back to the earliest days of powered flight.  It is important to remember that in the bewildering variety of aircraft shapes and sizes, the physics for stable and safe flight remain the same.
In subsonic flight rear wing placement offers the advantage of rear engine/propeller placement by which improves efficiency. However, this is offset by the need for much larger vertical and horizontal stabilizers, as stability torque arms are now much shorter.  Also of concern is keeping the pitch nuetral point behind the CG, which assists pitching nose down in a sink.  These issues plagued the Army Air Force Ascender design and was only remedied by adding more area aft of CG.  One silver lining is that this is not a problem with canard/delta designs, but deltas do not produce lift as efficiently as straight wings.  Careful checking shows that amazing speed and fuel consumption benefits comes more from weight savings of lighter composites than from futuristic swept designs,
though they are beautiful.
So for recreational aircraft the tried and true Piper Cub type design is one of the best one can pick.


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Which is the cable used in AFDX?
Avionics Full-Duplex Switched Ethernet (AFDX) is an avionics network patented by Airbus, developed starting with A380 and new standard in all new generation aircraft from Airbus factories.
I know that AFDX is Ethernet technology. But is it used the same Ethernet cable used to connect the computer to a LAN or to the Internet? Or is it used an improved version? Which are the differences between the two cables?

There are 7 levels of software and hardware commonly defined in networking standards. The top layer is called "application" and is the software you use, your browser, email etc. The bottom layer is called "physical" and is how the signals are transmitted from one place to another.  The "Ethernet" standard defines what the physical layer must do, but not how it must do it.  For example, Ethernet was invented and standardised long before WiFi which of course, transmits Ethernet signals with no cables at all.  "Ethernet cable" doesn't mean much. You mean a cable which can carry Ethernet signals.

I'm voting to close this question as off-topic because there is no explicit relationship to aviation. The OP needs to expand the acronyms, to make sure the relation is there, otherwise it's just a question about cable.

@Simon: Wi-fi doesn't relay Ethernet frames. Both Wi-fi and Ethernet are able to receive/deliver packets from the network protocol (often IP). While the OSI model is a reference, it doesn't depict well the TCP/IP world, it's more pre-IP and Telcos.

I agree that at first glance this question gives no evidence of being aviation related; it is however, since AFDX is an avionics network patented by Airbus. Voting to keep this open as on topic.

Thank you for editing the question to put the topicality to avionics forefront. Close vote is retracted.

ARINC Specification 664 calls for quadrax cable or fiber optic cable.  Quadrax is a four conductor matched impedance (100 ohm) cable.  Connectors are MIL-DTL-38999.

image source
The primary benefit is improved EMI protection and ruggedized connectors.
The B787 uses fiber optic.  A380 uses the quadrax cable.

So, it's not Ethernet cable? Why is it called Avionic Full-Duplex Switched Ethernet, then?

It's not the same as the cable connected to your PC, but that's not the same cable in the walls (plenum rated), nor is it the coax used in 10base-2, yet they are all "Ethernet".

You could theoretically use standard Ethernet cables on an a/c, but they wouldn't pass environmental testing or reliability/durability.

Physical layers for Ethernet are not limited to twisted pairs and unfortunate 8P8C connectors, but are multiple. Interestingly ARINC didn't chose one of them.

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How should a glider pilot signal turns to the towplane?
When in aerotow in a glider, I thought the correct way to get the towplane to turn right (say) was to move gently to the left. That would gently nudge the towplane’s tail to the left, which would then point the nose to the right and be a good signal that the glider pilot wants to turn right.
The FAA glider flying handbook displays the opposite technique in a diagram:

I don’t understand this. If you move right to ask the towplane to turn right, doesn’t that put the glider on the inside of the turn, and put you in the wrong place to follow the towplane around?
Which is the correct direction?

the inside turn has slower airspeed (good fir a high light glider) and not in the wake of the towing aircraft.

I learned to keep the tow-plane on the inside during my towing rating.

The glider flying handbook is wrong. The glider signals to the tow pilot by moving to the outside of the turn.
We glider pilots have been trying toget the FAA to fix this and many other errors in the GFH for years. See the newsgroup rec.aviation.soaring
Also, many tow pilots ignore tow steering directions because they think they know better than the glider pilot where the lift is.

Three Instructors at my local glider port Have repeated the same.

The turning radius R is given by,
$R \ = \frac{V^{2}}{11.26 \  tan \theta}$
where,

V is the true airspeed in knots
R is turning radius in feet and
θ is the bank angle in degrees

If the glider is turning at a radius greater than the tow plane, i.e. it is in the outside of the turn, it must be flying at a higher speed in order to complete each circle in the same time. For glider in the inside turn, the opposite is true i.e. the glider is flying at lower speed compared the tow plane.

Image from FAA Glider Flying Handbook
Also for outside turn, the bank angle of the glider should be higher than the  tow aircraft to compensate for the higher speed. The reverse is true
for an inside turn.

Image from FAA Glider Flying Handbook
Therefore, the only way the two aircraft can fly coordinated with the same bank angle is if they have the same speed and turning radius.
Flying the glider in inside of a turn is preferred because it is easy to give corrections (to have same speed and turning radius) compared to outside turn. The glider bank angle can be reduced till it returns to the correct position. Since the glider is flying at a lower airspeed (than the tow plane) it will accelerate as its turn radius increases so there will be no tendency for slack to develop in the tow line.
For gliders in outside turn, the bank angle has to be increased to reduce the turn radius. However, as the glider is flying faster compared to the tow plane, it (glider) will tend to overtake it as turn radius is reduced, developing slack in the line unless airspeed is also reduced (usually by yawing the glider away from the towplane). In this case, the correction process is more difficult.
For this reason, it is advisable to

...match the tow plane bank angle and point the nose of the glider at the tow plane's outer wing tip.

at-least for small bank angles.
In general, it is better to be in the inside of turn rather than outside:

If you have to err on one side or the other, it is better to err on the inside – especially when at a low altitude. This way, you’re not in as much danger of locking out.

as long as you are not too far inside so as to sink and stall.

this is some useful content, but my primary question is: which way to go to indicate a turn to the towplane, and less what to do when the towplane is turning.

@Peter I'm sorry I misunderstood your question. There are two versions of this signaling, of which the soaringsafety version makes more sense to me. Apparently there have been efforts to correct the handbook.

Land-lubber question here: if the glider turns slightly to the right, causing the tow plane to yaw left he will correct with right rudder then turn right. Slight risk of sideslip. But if he turns left with the left yaw the risk would be for a skid, which is worse - am I correct? Also if the glider turns right he would be at a right bank. If the tow plane then pulls him left it would put the glider at an extra high aoa. All this can be corrected with control, but an outside turn seems to have a slightly higher risk of instability and would require more aggressive control inputs.

This has nothing to do with signaling the tow pilot to make a turn

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Why is it rare for small aircraft to have winglets?
I've noticed that winglets are very rare on small aircraft. I wonder why this is the case. Wouldn't they have the same advantages, especially because they travel at low speed? Or is it just a wrong impression I got and they aren't that rare?

My general understanding is that winglets can be best optimized for aircraft that spend a lot of time in a rather narrow window of possible angles-of-attack-- eg an airliner in long-range cruise.

I've talked to a couple of aerodynamicists, and for small aircraft when you run the numbers the improvement offered by winglets is often less than the drag penalty caused by their weight (which also reduces allowable payload). For larger aircraft that fly long distances, the proportion of the aircraft's weight that is due to the winglets is much smaller than it is for small aircraft, so they don't have this problem and that makes winglets a viable strategy.

Seems to be the more pressing argument against it so I changed the accepted question. Sorry Jan Hudec...

@qq jkztd it may be that that the winglet increases lift efficiency enough to allow the same lift at a fraction less AOA, meaning less drag.  The winglet is a fence.  Interesting that the 737 has them both up and down (with the supercritical wing).

Similarity of gliders and airliners is high aspect wing (easier to bend and twist).  Digging into this further, and reading about the entire wing downwash rolling up, it may be true that the winglet does not make this vortex significantly smaller, but it may get it farther away from the lifting surface, reducing drag producing oscillations from turbulence.  There are a few possibilities as to why they work, now trying to quantify them.

As others have pointed out winglets don't make much aerodynamic sense for small aircraft.
The point of a winglet is basically to deflect the wingtip vortex away from the lift-producing part of the wing, granting an increase in effective wing span without the added form drag of actually making the wing longer.
The winglet itself creates some form drag though, and it adds weight. On most small aircraft the potential improvement in wing efficiency doesn't exceed the  weight and form drag that result from adding the winglet.

What you will find on many small aircraft are Hoerner-style wingtips (either installed at the factory or added later through an STC modification). At lower speeds these have aerodynamic benefits similar to winglets, but without the additional form drag, and usually little or no added weight.

So if Hoerner-style wingtips offer similar benefits to winglets without the drag/weight, then why aren't they used on larger aircraft?

Because winglets can provide more benefit on longer range aircraft than these wingtips, and there are other options as well (see 777 or 787). Things can be different in the upper Mach numbers.

Pretty much what @fooot said -- at higher speeds and with larger wings the wingtip vortex would be comparatively larger, and would still "spill over" onto the lifting surface with Hoerner tips (they would be an improvement over a "plain" rounded wingtip, but winglets are a further improvement over the Hoerner-style tip). There's a crossing point where the winglet becomes more efficient than the Hoerner-style tip, but where that is depends on aircraft/airfoil design, expected cruise speeds, etc.

I get that, but it isn't clear in your answer (so you may want to clarify it a bit.)  :-)

First, winglets look fancy but will not help that much in drag reduction. They were pushed less by engineers than by marketing, Boeing's in particular. They help a litte in ideal conditions, but in sideslip or at high speed they can quickly increase drag.

Then, most small aircraft are designs from a pre-winglet era. Adding them means to invalidate the type certificate, unless someone takes the initiative to re-certify the aircraft with winglets. I guess nobody has seen this as a profitable endeavor so far.

Gliders benefit from winglets because in competitions they are grouped in classes. Membership of some classes is defined by wingspan. Gliders get better with increasing wingspan, so if regulations limit the lateral extension, the way out is to extend the wings upwards. If there is no such artificial limit, it will in most cases be better to expand the wing in spanwise direction.

+1 for the second paragraph. Would accept your answer too if I could but Jan Hudec wins this one for beeing a little more extensive.

I've actually seen real world numbers from the same airliners, 737s, 757s and 767s pre and post-winglets. This was internal information at my airline. The number showed that winglets paid for themselves in about a year, including all of the modification costs. Airlines weren't installing them when they were headed to bankruptcy because Boeing is good at marketing. They do what they claim to do, and at an airline, 4% is huge.

@OSUZorba: I bet this was for the 737 winglets. Look at that wing: It has been pushed way above its design lift and adding winglets will help to shift the operating point back to where it was supposed to be. Now compare this with a new wing - the benefit is very small.

737s had the largest improvement, but the 757s and 767s still paid for themselves in about a year. A little less than a year for 757s and a little more for 767s. I agree that winglets make the most sense on an existing wing that can't be changed, however, there are generally other limitations on wingspan than pure aerodynamics, such as aircraft design group link and gate size. Of course, these limits will have less impact on GA aircraft.

@OSUZorba: And they were operated at the same cruise Mach number, same altitude, same routing? No additional changes, like to the engine control laws? Thought so. You are comparing the winglets not on an equal basis, but a bunch of fuel-saving changes to the situation before. The winglets were only part of this. Didn't I tell you they are good at marketing?

Considering they came into mod and left mod and the only thing done was winglets, and the aircraft fly about 300 hours a month, and it was over 400 aircraft by the time it was all said and done. It is pretty easy to build a statistically significant representation of what was going on. Unless you think the entire routing of the entire system changed once winglets were installed. Like I said, I've seen the real data, from real aircraft, flying real routes. Winglets on existing commercial designs are far more than marketing to a commercial operator.

Many small aircraft designs are rather old and winglets were not common on airliners either when they were certified. For airliners that fly 8 or more hours a day saving a few percent on fuel quickly pays off the additional development and certification, so winglets were adopted quickly there. But typical general aviation aircraft does not fly anywhere close to that and the few that fly more and would be worth upgrading (and their owners have money for upgrade) are not enough to make the design and manufacture profitable.
Note, that winglets did find their way to gliders, especially competition ones, as the little benefit is more noticeable there. They also do appear on some newer designs, most notably the Diamond ones (DA20, DA40, DA42).
The situation is very similar to why we don't see more aircraft diesel engines. They are more efficient, use cheaper fuel and are somewhat cheaper to maintain, but the certification is so complicated that there are only few modifications available.
Also most GA aircraft are not really very efficient to begin with. The DA20-A1 claims glide ratio 14:1 and that is way better than most competitors. Compare with airliners where 18:1 is nothing special (was claimed by A320 some 30 years ago). So winglets are not going to help as much.

The chief designer of DA comes from a glider background and knows winglets in and out. On the other hand, more conservative designers do not embrace winglets openly. When Rutan's Starship design was forced upon the engineers at Beech, the winglets were a major source of their many complaints, which mostly turned out to be correct, btw.

@PeterKämpf Your comment made me curious to know what were the major complaints with winglets and which ones turned out to be correct?

@Canuk: The biggest complaint: Now the bending moment at the tip is not zero anymore. But the winglets were not their biggest complaint; the Starship prototype was shoddily built such that the wing thickness differed between left and right wing, for example. Management insisted that it be copied completely from the 0.85 scale prototype, warts and all. This was most upsetting.

RE immediately above-- they insisted that the mistakes be copied? That is bizarre and almost hard to believe.  A bit of trivia: one of the lead engineers on the Starship project was my glider instructor when I was a kid in high school.  Maybe that explains why I find I have an unconscious tendency to always push on one rudder pedal?  (Kidding!)

They also appear on paraglider wings which are definitely small aircraft.

One possible explanation is that large amounts of sweep and higher indicated airspeed are less common in "smaller" GA aircraft.  Larger and faster aircraft with large amounts of sweep literally plow the air aside, resulting in a significant spanwise airflow at the wingtips.
Winglets are touted for reducing the strength of wing tip vortices, and are said to generate some forward force from the wingtip vortex, but they also may improve efficiency simply by bouncing the span wise flow aft, which would generate a small amount of thrust.
The winglet "fence" may also allow a slightly lower AOA for the same amount of lift by helping maintain pressure differential all the way to the wingtip.  Lower AOA means less drag.
An earlier form of winglets, wing tip fuel tanks, also served as a wing tip fence in addition to acting as a wingtip weight roll damper and spanwise weight distributor.
Many smaller, slower planes do not benefit enough from winglets to justify the additional cost and weight.  However, they may be seen on STOL aircraft to help trap a bit more air under the wings for high AOA slow flight, along with slats and flaps; and more competitive gliders, where a slight advantage is meaningful.

My general understanding is that winglets are most beneficial for aircraft that spend a lot of time in a rather narrow window of possible angles-of-attack-- e.g. an airliner in long-range cruising flight.  Small aircraft tend not to fit this profile, unless they are flown by really boring pilots.


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What item is a pushback operator holding up after pushback?
After a pushback I saw the operator of the pusback truck standing next to his truck and showing the pilots a "thumbs up" with his right hand. In his left hand he was holding something up. It looked like a key or some kind of cotter.
I could imagine that it is some kind of part that he could only have if he really is clear from the plane and didn't forget to disconnect something.
Am I right? Is this some standard procedure? If so, what was he holding?

From the title in Hot Network Questions, I thought this was going to be a pushback operator being the cause of delays, not physically raising an object in his hand.

@corsiKa I actually had to look that up because I'm a non native speaker and to me it sounded like that too. Also: it was on hot questions? That's the second time I made it and both were on aviation. Sweet :D

@corsiKa Fixed it for you.

It's a steering bypass pin which isolates the nose wheel steering and enables the tug to turn the aircraft.
The operator holds it up so that the captain can see it to confirm that it has been removed.
This Wikipedia article refers to it
On some types, there may also be a "downlock" pin which prevents the nosewheel gear from retracting whilst the aircraft is on the ground.  In this case, the captain is looking for 2 pins being held up.  More often though, the ground lock pin(s) are removed before pushback and stowed onboard.

Allright, that's pretty much what I thought. I actually read that Wikipedia article last week after the flight but somehow missed that part. It was really late though ;-) Thanks!

I wonder how many aircraft have taxied straight into the green after pushback until this procedure was invented :-)

The last sentence mention ground lock pin stow on board. How is it put in place after landing? Pilot climb down and hand it to engineer?

The downlock pins are not normally fitted.  They are only fitted during maintenance and when towing without hydraulic power.  The ground crew are responsible for fitting them and removing them, and a tech log entry to that effect must be made.  The flight crew simply check that they are in the stowage as part of the pre-start checks.  They would be very obvious during the walk-round anyway since they have long red flags attached with "remove before flight" printed on them.

As you do not provide a photo, I have to speculate, but I do not see many options.
The operator was probably holding the connector that allowed him/her to speak with the pilots, at the end of the pushback the connector is disconnected and the thumbs up is given to confirm the all clear to the pilots (no verbal communication is possible at this point).

Sounds plausible. It could have been that connector although I didn't see much of a cable. I was not quick enough to take a photo :-(


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How to record Intercom / ATC in a small aircraft like a Piper Archer?
For making videos it would be nice to have some more sound than the engine sound recorded by my GoPro. What ideas do you have to record the aircraft intercom? It won't be a problem for me to have two files (an audio and a video file).
Edit: I'm looking for a good sound quality comparable with that which you will have while sitting in the aircraft listening to the intercom.

invest in a CVR?

Plug into an unused headphone jack, use a size adapter to plug into your recorder's microphone jack, and record.

For the GoPro specifically there are audio recording cables you can buy which connect to your intercom jack and provide a pass-thru connection for your headset.
There are other cable options available to support recording on different devices (e.g. iPhone/Android phones and tablets).
As is often the case with "aviation" accessories these can be somewhat expensive, but they're also pretty reliable drop-in solutions. As mah noted if you have a spare headset jack you're not using plugging into that can be much cheaper and just as effective.

Good answer. Just note that aviation intetcoms have a very high signal level to drive high-impedance (600 ohm) aviation headsets; this is much higher than consumer audio levels. Enough to blow some devices if they can't handle it and the cable does not provide any impedance matching.

Thank you for this -as allways- very helpful answer! As this peace of equipment is designed for this use it should be no problem. Anyway, Iif you have more information about this I would be really curious because I'm really inexperienced in terms of audio recording. Another question would be if there would still be the aircrafts sounds on the recording.

The specialized aviation adapter cables are fantastically overpriced (there must be a law somewhere that companies are required to rip-off aviation consumers). Assuming you have an open headset port on your intercom, save yourself a few bucks and just buy a 1/8 to 1/4 TRS cable. You can get it on Amazon for less than $7.
Unfortunately, if you have the Hero 3, you're still stuck getting a USB audio input adapter (you would need this for any type of external audio input anyway). But even then you're only out 17 bucks, versus spending $44 (!) for a specialized cable.
Regarding the high signal output, this doesn't appear to be a problem with the GoPros; I've successfully recorded a bunch of flights this way with no issue. Besides, as far as I know, none of the specialized cables provide any type of impedance matching either.

Find a small microphone or even an earbud speaker that will plug into your recorder's IN jack.  (The earbud will in most cases work like a microphone).  Then just wear it inside the earcup on your headset.

Is that really the way you would go about solving the problem? Your recorded signal would most likely be horrible, and your ear might also be uncomfortable. If you don't have a spare headset jack available (single seater, or all seats occupied with passengers using headsets), a splitter wired to the recorder's mic input would be orders of magnitude better.

Yes, it is.  Start with the easiest, least expensive solution I can think of.  If the results are not satisfactory, then escalate complexity and expense.  How is this not a good plan?

It's not a good plan because it's an almost certainty that the recording quality will be unusable. (While an earphone can work like a mic, they're not the same device and quality will suffer greatly.) Also, unless your mindset is that there simply aren't any unused headset jacks left in the aircraft, it would be very surprising you don't consider using an empty jack simpler. While purchase of a size adapter in order to use an empty jack is not free, the few dollars would hardly give "least expensive" much merit.

Neither you nor I know what Falk requires with regard to the quality level. With that, I will let Falk do as he pleases, and at least he has options.

-1, I'm sorry, I agree with @mah - this is not a good solution.

The idea itself isn't bad at all, but I'm afraid that this would be very uncomfortable, especially as I'm using a quite thin headset without a lot of extra room between the headset speakers and my ears. I won't criticize your answer because of the most probably poor sound quality - for flight training and analysis this would still be a good and economic option. Anyway, my training is finished now and I'm interested in having good quality sound for cockpit videos. I will add this to my question to avoid further confusion.


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How does the efficiency of a piston aircraft change with altitude?
Turbine aircraft are more fuel-efficient, per mile, the higher they fly and this is for two reasons:

drag depends mostly on indicated speed, but the same indicated speed corresponds to higher true speed, and
the lower temperature increases efficiency of the engine.

Now both effects should also apply to piston-engined aircraft. Plus

spark-ignited engines are more efficient with open throttle, which again occurs near operating ceiling.

So I would expect piston aircraft to also fly as high as possible, and most piston aircraft should have no problem to get to at least 10,000 ft (where supplemental oxygen is not needed yet). But in various stories and documents I notice even long flights are often made much lower. Below 5,000 ft.
So is there actually some reason why piston-powered aircraft would be more efficient at lower altitudes? Or any other reason to prefer flying low?

Higher altitude is a lower fuel consumption rate, but also lower BHP for the manifold pressure. This basically means that the lower you go, the more fuel you burn but the faster you travel. So if you are OK running (Ex: IO-360) 2200 RPM/17"MP and 100 KTS, vs 2500 RPM/21"MP and 142 KTS, that is a choice the pilot makes. Plus, even if O2 isn't needed, doesn't mean you won't feel its effects after 2-3 hours in a low-oxygen environment, it feels a lot like a bad hangover and I'd rather fly lower than require monitoring of my blood-O2 every 15 minutes and feel like junk the next day.

Regardless of what happens with aircraft where the propellers are optimised for lower TAS, the lower temperature at altitude and the combination of best polar point (minimum drag) and full throttle conspire to make piston aircraft more efficient at higher altitude if the designers don't mess up.

@PeterKämpf, I would think it should, but why then the graphs in ymb1's answer suggest otherwise?

@JanHudec: Hard to say without knowing the airplanes. Maybe the prop twist was a compromise between good take-off distance and cruise, so efficiency suffers at high TAS, or the power demands for cabin heating and pressure cost more fuel at higher altitude. The better efficiency of heat engines in colder air can only be exploited when the peak cycle temperature does not change - now I would need to know the details of how the Wright 3350 were run. Most likely the result is the sum of many small effects.

You are right, flying higher will be more efficient. However, the inverse relation between thrust and speed in propeller aircraft means that the available speed range is much smaller, and thus the possible altitudes are more restricted. Simply put, the possible gains are smaller.
If you look at the thermodynamic cycle of a turbo-compound engine, it looks almost like that of a jet. Still, the high bypass ratio translates into a lower optimum flight speed and the lower power-to-weight ratio usual for piston aircraft limits the maximum altitude and makes them more susceptible to adverse winds. Also, turbo-supercharging, which is much more efficient that supercharging, was developed to a practical solution only a few years before gas turbines were introduced, so pre-WW II piston engines relied on the less efficient supercharger for boosting power, reducing the benefit from flying higher yet again.
Why historic flights were performed at lower altitudes has probably more to do with the low ceiling of the initially heavy airplane and the lack of supercharging than with a deliberate choice by the crew. Maybe the lack of cabin heating or de-icing equipment, or even an open cockpit, made lower, warmer altitudes also preferable. Another reason might be the need for terrestrial navigation in the absence of today's infrastructure of radio beacons and GPS satellites. That flying higher translates into better range was known as early as WW I.

dead link for turbo-compound engine

@ivoWelch: Try the new one, it looks like they moved the page.

Ron Beyer's comments are good ones. In addition:
There are, for these purposes, two sorts of piston engines: normally aspirated and turbocharged. Normally aspirated engines use ambient air: the air pressure out in the atmosphere is what the engine feels (ignoring flow inefficiencies in the intake system and effects of ram air). Turbocharged engines use an air pump to maintain or increase the air pressure into the engine. A normally aspirated engine's maximum power output decreases as altitude increases: increased altitude yields decreased pressure, and with the nearly-constant proportion of the atmosphere made up by oxygen (21%), the amount of oxygen in the air drops. If the engine is operating at maximum available output and efficiency, if you decrease the oxygen you decrease the fuel, and decreasing both of these will decrease available power, all else being equal.
A turbocharged engine can maintain full sea-level manifold pressure (air pressue at the intake) to altitudes above sea level. How high they do this depends on the specific engine installation: some, only to 10,000', others to over 20,000'. Maintain the air pressure and fuel flow and you maintain the power output.
A turbine engine is, for these purposes, normally aspirated. Altitude goes up, maximum possible power goes down. Many turbine engines are thermodynamically capable of generating more than their rated power (termed "flat rating"), being limited in some other way. These engines can maintain rated power to higher than sea level altitudes. Essentially, this is like running a piston engine at partial power when at sea level—say, 20" of manifold pressure, instead of the normal sea level maximum of 30"—but being able to maintain that power up to perhaps 10,000'.
If you can maintain desired cruise power, true airspeed increases with altitude. It goes up at about 2% per 1,000'. Most of today's piston engines are run between 60% and 75% of maximum power while in cruise, and it turns out that is generally the maximum available from the engine at somewhere between 7,000' and 12,000', depending on the installation. Aircraft with turbocharged engines fly under different constraints.
Take my Mooney 252 as a specific example. The engine is turbocharged (turbo-supercharged, to be more specific: the turbocharger can maintain higher than sea level manifold pressure, and the engine is rated for a maximum of 36" manifold pressure), and I can maintain full power to about 20,000', and a high-speed cruise power setting of 75% to 25,000'. The higher I go, the higher my true airspeed.
There are other considerations besides oxygen, even beyond Ron's note about low level hypoxia, including wind, weather, practicality, and pilot training and comfort.
Wind often increase with altitude. When I fly eastbound (or otherwise with the wind), that's a good thing; when westbound (or into the wind), that might be a bad thing, and higher altitudes might yield LOWER ground speed, because sometimes the wind speed increases with altitude more quickly than my true airspeed.
As to weather, sometimes it's better to fly below the weather than through it, especially when there are embedded scattered or isolated thunderstorms. There's airframe icing to consider. Turbulence might be present at higher altitudes and not at lower.
From a practical standpoint, there might not be net benefit from climbing high, even higher than 5,000'. Or, that benefit is minimal. While climbing, you're flying slowly, more slowly than cruise. You don't gain this back in the descent. You also burn more fuel per mile, which, again, you don't gain back in the descent. For a short flight, maybe it will take more time to climb to 7,500', or to 10,000', than you would save from the increased true (and ground) airspeed.
Acute hypoxia won't be an issue for most people at 10,000', but, as Ron mentioned, flying for 2-3 hours at 10,000' without supplemental oxygen can result in low-level, sub-clinical hypoxia, causing, in some people, headaches, decreased visual acuity (especially at night), and diminished cognitive function.
One other reason to fly low: see the sights!

The whole discussion about aspiration is irrelevant. Power decreases with altitude, in a similar way in all types of engines and supercharged engines are simply flat-rated. Nothing of this affects the fact that thermodynamic efficiency is best near the operating ceiling (which is different for each aircraft, but that is not subject of the question).


text:
Can a modified aircraft be imported and certified in the US?
Aircraft can be brought into the US and be made airworthy by FAA standards. What about aircraft legally modified in other countries?
For example, there is a new STC to put a Rotax 912 into Cessna 150s approved by the EASA. Can that STC be made legal in the US even though no similar STC exists here?
If yes, is this just due to relations between the EASA and FAA, or can this be done with aircraft coming from anywhere?

AOPA has a lengthy article on the subject of importation but I don't think it really answers my quesion. http://www.aopa.org/Pilot-Resources/PIC-archive/Aircraft-Ownership/Business-Justification/Importing-and-Exporting-Aircraft

as long as you are willing to follow through with the certification process I don't doubt they would allow it

@ratchetfreak but what is the process? A normal person couldn't afford to do the full STC certification process. A one-time 337 approval might work but that's not really an "official" way to do it since there's no guarantee it will be accepted.

Well, pretty much anything can be given a US airworthiness certificate provided it's not literally falling to pieces.  You could certificate such an aircraft as a Special Airworthiness Certificate in the Experimental category -- Specifically one of:

Experimental -- Research and Development
  To conduct aircraft operations as a matter of research or to determine if an idea warrants further development.  Typical uses for this certificate include new equipment installations, operating techniques, or new uses for aircraft.

or

Experimental -- Showing compliance with regulations
  To show compliance to the airworthiness regulations when an applicant has revised the type certificate design data or has applied for a supplemental type certificate or field approval.

If your goal is to ultimately get this aircraft a Standard airworthiness certificate you would probably want the latter, to allow you to conduct test/certification flights in the modified aircraft.
To then get a standard airworthiness certificate things are a bit more murky. You could get a US STC based on the European STC & using this aircraft as the example for conformity inspections and flight testing, but that would require going through the STC process.
The other option would be the 337 process, in which case you are also going to need an A&P mechanic (preferably one with Inspection Authorization) and the cooperation of your local FSDO to approve the modification as a "major alteration" (FAA Form 337 - Instructions here).
As you alluded to in your question, something like installing a Rotax engine in a Cessna 150 is a "Major Modification" that has no "FAA Approved Data" (STC procedure/drawings/etc.) to include with the 337, so you would need to submit "Acceptable Data" for your modification (the European STC is a good starting point) and work with the FAA to obtain approval for the modification.

This is something you would want to talk to the FAA about before purchasing an aircraft with such a modification (there's a good chance they may not approve the modification, which would leave you with an unairworthy aircraft, or one restricted to the Experimental category).

This is pretty much the answer I expected. Aircraft certification is such a convoluted business...

@StallSpin It's actually not all that bad - If you BUILT a Cessna 152 from plans & installed a Rotax engine in it the FAA would rubber-stamp your "Experimental - Amateur Built" airworthiness certificate after a few flight tests. What makes this case more painful is you're modifying a certificated design (in such a way that it no longer conforms to its type certificate or an approved supplement - both of which would have had appropriate flight tests proving their safety).

If I were faced with this problem, my first call would be to the EAA, the Experimental Aircraft Association.

If the aircraft you import to the US was certified by country that the US has a aviation bilateral agreement with (https://www.faa.gov/aircraft/air_cert/international/bilateral_agreements/baa_basa_listing/) your ability to import the aircraft would be improved and much easier because the BASA (Bilateral Aviation Safety Agreement) among many things recognizes the other country's certification process with focus on certification differences such as the STC you mentioned (e.g. Issue Papers and Certification Review Items). The US does have a BASA with EASA.


text:
What are the advantages and disadvantages of ruddervators?
Can someone clearly explain the advantages and disadvantages of ruddervators? I cannot find the answer anywhere else.

closely related

More induced drag
A disadvantage (especially critical during landing) is that there is more induced drag to make certain movements.
The image below helps to understand this:

Source
To yaw, you have to use both ruddervators (contrary to just a single rudder movement for a normal tail). This is done in order to compensate the unwanted vertical component. This leads to increased induced drag, which is a big problem during take-off.
Less interference drag
The number of intersections goes down. In the case of a conventional tail you have three intersections (fuselage - left elevator, fuselage - rudder, fuselage - right elevator), whereas for a V-tail you only have two (fuselage - left ruddervator, fuselage - right ruddervator). This reduces the interference drag.

The main advantages of the ruddervators (or V-tails are)

They are typically lighter and have less wetted surface area compared to the conventional tail configuration as it has one control surface less (though this reduction is not as simple as reducing one third). As a result the drag is reduced.
They are used in some cases to increase stealth. The canted surfaces reflect the radar away from the source, aiding in stealth. They also allow the engine to be mounted above the fuselage (like Global Hawk), reducing the infrared signature from below.
In Cirrus SJ50, the 'V' tail is used to allow engine placement above and outside the fuselage,which is claimed to improve safety and reduce cabin noise.

The main disadvantages are:

They require a much more complex control system compared to the conventional aircrafts as both the surfaces have to be move together.
They are required to be structurally more robust compared to the conventional system due to the increased load involved. This reduces the advantage gained by eliminating a control surface.
The amount of control forces required for operating the ruddervators are higher compared to the conventional ones and in some cases, it may be more.

it has one control surface less what? 1 elevator and 1 rudder vs 2 ruddervators. how is there one less control surface?

@ Federico 2 elevators & one rudder.

Even on stealth aircraft, V-tails are still generally flat rather than curved, so the surfaces should still reflect radar just as well as vertical or horizontal tail surfaces - just with the optimum radar position in a different location.

@Sean not necessarily - the problem with the regular arrangement is that the surfaces are at 90 degrees to each other, forming a corner reflector. The ruddervators on stealth aircraft will be at a greater angle, making the returning beam miss its origin. (Among other effects.)


text:
Can fuel be stored in the anti-shock bodies?
lets say an airplane needs to get to a certain route but doesnt have the fuel to do and it needs to store in the anti-shock bodies. Is it possible?

Fuel is stored in fuel tanks, which typically have two requirements:

They must be sealed so as to contain the fuel in all probable flight attitudes.
(Ideally they will keep it contained in a few  improbable ones too.)
They must have appropriate plumbing to get the fuel to the engines.
(There are some exceptions to this, but fuel in a tank you can't use is not helpful in flight.)

Anti-Shock bodies are typically not fuel tanks - they meet neither requirement as they are not watertight (fuel will just pour out of them), and there's no plumbing to get the fuel out of, or for that matter into them.
As "Exhibit A", take a look at the anti-shock bodies around the 787 flap tracks & actuators- Note that the anti-shock body is hollow, but unsealed. Any fuel (or water) in here would simply pour out the trailing edge when the flaps are extended.

I guess the more interesting question would be: Is it feasible to seal these hollow bodies to make them watertight? The additional plumbing would definitely need changes but does not seem too onerous. The real crux is "Is it worth it?" If one really needed more fuel to add range I'm sure expanding the primary tanks themselves or adding a fuselage tank might give you more bang for the buck than squeezing in a few hundred liters into the shock bodies.

@curious_cat As you'll note from the photo the anti-shock bodies on an airliner wing may be hollow but they aren't empty (there are already hinges, actuators, hoses, etc. in them, all taking up what would be fuel capacity). By the time you got done sealing the area (in such a way that doesn't interfere with its normal movement in flight) and adding plumbing you probably wouldn't get much usable fuel out of the equation. A bigger tank in the wing or fuselage generally wins out in design.

@curious_cat: Well, if your antishock bodies aren't being used as flap-track fairings or what have you, using them for additional fuel tankage is perfectly feasible, but not many airliners today have antishock bodies that aren't already playing double duty as something else.

Yes, and there have been cases of this. Tip tanks of the period when aircraft flew already supersonic and jet engines were still very thirsty are a good example. Below you see the area-ruled tip tank of the F-5.

F-5 tip tank (picture source).
Now that @voretaq7 got me thinking, I should also mention the "Doppelreiter" fuel tanks (slipper fuel tanks) which were used on some German fighter airplanes in WW II. They were mounted above and behind the wing, and to everyones surprise they had little impact on the top speed of the airplanes, and in case of the Me-309 helped to increase it slightly. They were the first practical application of Küchemann carrots and worked much like the flap track fairings of today's airliners.

FW-190 A with Doppelreiter tanks.

Not sure if that's quite what Ethan was asking about (I took his question to mean repurposing anti-shock bodies around other fuselage protrusions), but certainly if you're forced to have a fuel tank that can't be embedded in the wing or fuselage you want it shaped to create the least drag possible (we saw the beginning of this with even older designs, this drop tank from WWII for example).

@voretaq7: Yes, Ethan probably thinks only of the flap fairings, but tanks are good Küchemann-bodies in their own right. Messerschmitt experimented with additional fuel tanks which were put on top and aft of the wing, and to everyones surprise the planes flew faster with them than without. They were called "Doppelreiter" and were the first practical Küchemann-bodies.

In at least one case, yes!
The Convair 990 jetliner (a derivative of the earlier Convair 880) had large, prominent antishock bodies on its upper rear wings, easily seen in this photograph of a retired NASA 990:

(Image by NASA, via Stahlkocher at Wikimedia Commons.)
These antishock bodies - particularly the larger inboard ones - also served as fuel tanks, and held the aircraft's fuel-dumping apparatus.  Wikipedia sums it up nicely:

One change from the 880 was the large anti-shock bodies on the upper trailing edge of the wings to increase the critical Mach and reduce transonic drag. The inboard shock bodies, which were larger, were also used for additional fuel tankage. Later during the design period, Convair modified the design to include fuel in the outboard pods as well, but during the initial test flights the extra weight caused the outboard engines to oscillate in certain conditions. The pods were redesigned once more, and shortened by 28 inches (710 mm), causing increased drag. The inner set of pods also served a secondary role as fuel dumps for the fuel tanks, and the outlet pipe is prominent.


text:
Under what circumstances is an FAA accident report required?
Under what circumstances is an FAA accident report required?  For example, if two planes are pushing back from a terminal and their wings collide is an accident report always required or does it depend upon damage done to the aircraft?

"Am just asking for a friend ..."

Generally you do not notify the FAA, you notify the NTSB (the relevant regulations are in 49CFR, specifically 49CFR830).
If you notify the FAA they will contact the NTSB, because the NTSB is the agency charged with investigating aircraft accidents.
If you crash in a cornfield somewhere and notify the NTSB they will probably ask the nearest FSDO to send an investigation team (unless you're a major airline or a fairly high-profile incident).
So ultimately it doesn't much matter which agency you call, but you should be calling the NTSB.

With the administrative stuff out of the way, the reporting requirements are also in that same section of 49CFR. Basically they say:
You are required to notify the NTSB "immediately, and by the most expeditious means available" of any aircraft accident, which is defined as:

…an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage.

You are also required to notify the NTSB (again, "immediately, and by the most expeditious means available" of any incident (something that's not an accident as defined above) which meets the following criteria:

Flight control system malfunction or failure;
Inability of any required flight crewmember to perform normal flight duties as a result of injury or illness;
Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path;
In-flight fire;
Aircraft collision in flight;
Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less.
Specific requirements for aircraft with a takeoff weight above 12,500 pounds
Release of all or a portion of a propeller blade from an aircraft, excluding release caused solely by ground contact;
Specific requirements for "glass cockpit" displays.
Specific requirements for TCAS advisories.
Damage to helicopter tail or main rotor blades, including ground damage, that requires major repair or replacement of the blade(s);
Specific requirements for air carrier blunders like landing on the wrong runway.

"Immediately and by the most expeditious means available" basically means pick up the telephone and call them: They don't want you dispatching a letter via Pony Express that's going to take a week to get to the NTSB's headquarters while the aircraft is sitting in a field exposed to the elements with evidence literally washing away in the rain.

What  is  FSDO?

https://en.wikipedia.org/wiki/Flight_Standards_District_Office


text:
Why are dirt and bugs on an aircraft so bad?
It's noted in many POHs to keep your aircraft clean all the time, but is there a reason to this?  Dirt hardly add any sort of weight to the aircraft, bugs are extremely small and other things such as cars easily move even when dirty as a mud pig.
Does having dirt or bugs on your aircraft seriously affect the structure or performance signficantly?
If so, why?

...you mean besides the fact that they look ugly? :-)

@voretaq7 that is the difference between car and aircraft owners: their washing behavior is compulsive, ours is just common sense (look at my car if you don´t believe me) :D

For (modern) gliders with highly optimized laminar flow airfoils, bugs (or dirt) are a non-negligible factor, especially in competition gliding. There are some older laminar airfoils that are notoriously allergic to bugs (and rain), but all are to a certain degree. This is also the reason why any glider pilot worth his or her salt will painstakingly clean their ship each afternoon and before each competition flight.
Sufficient bugs will degrade your performance by a noticeable amount - most gliding computers even have a special "bug" factor to include that into glide path calculation (even though the measuring and correllation of that is quite subjective). I´ve had a few flights in somewhat biblically bug-infested conditions (summer, hot, low thermals) that more or less painted the leading edge black (like in this picture from an article on the DG Flugzeugbau website).

Bug wipers are quite common on high-end and competition gliders and can be found e.g. at http://www.storka.at/. Or try to google for "Mückenputzer". Of course bug wipers are not without drawbacks (concerning cost, installation, ease of use, drag etc.). A friend of mine once stuck a banana peel on his wing and tried to remove that with the wiper, resulting in banana and wiper being stuck in the middle of the wing. It took some creative maneuvers to clear that mess, by which time probably a lifetime aerodynamic benefit of cleaning had been spent.
As for the comparison with cars, their aerodynamics differ in a lot of ways. In comparison to a wing there is no laminar flow to talk of at higher speeds (most of it is turbulent), which drastically reduces the influence of the surface smoothness on the drag produced.

That's very interesting, I had no idea that this is such a big concern for gliders

@Pondlife fun fact: On many a gliding field you´ll see the most soiled cars (in&outside), while the planes are gleaming :D If you want an insight on how passionate you can get about your ship, listen to the very interesting podcast about Dick Butler´s Concordia.

@yankeekilo: Why do you use that weird kind of apostrophes?

@Dan those are the ones that are often  used in German.

@yankeekilo: I see. Coincidentally, I've just met another German online, who realized he was making the same mistake.

One of the main reasons why it's not a good thing to have dead bugs on the windshield is that it becomes very difficult to spot other traffic. Other planes are just little specks at a distance and when your windshield is covered with specks from dead bugs it becomes very difficult to spot another aircraft in the distance.

Ah yes I forgot about the "Is that a dead bug or a head on" phenomenon

Bugs or other dirt can have several effects on a (light) aircraft:

It will have some effect on airflow, however slight
It may affect the paint or surface by corroding or leaving stains
It can block pitot tubes or other openings
It can build up on windows and obstruct the view
A heavy buildup of dirt could make the brakes less effective

The effect of dead bugs on airflow is probably negligible (frost or ice would be a different story), but a blocked pitot tube can be very dangerous because the airspeed indicator will read incorrectly. Dead bugs on the windscreen may seem like a minor issue, but even a small blind spot could hide another aircraft and prevent the pilot seeing it.

A lot of bugs on the leading edge of a wing does significantly degrade performance. Years ago I gave a lot of float plane instruction in a J3 with an 85 hp engine. If the student was heavy and there were a lot of bugs, it wouldn't fly. Clean off the bugs and it would.

That's potentially because bugs would create disturbed air and detach the flow from the top of  the wing quicker then it would normally happen. So lift is significantly reduced.

Mud dauber wasps are credited for at least two total losses: Birgenair Flight 301 and Florida Commuter Airlines Flight 65.
Airfoil soiling can make a large difference to performance. I don't operate aircraft, but I have operated wind turbines. Older stall-regulated wind turbines can take a performance hit of 20% if they're not kept clean.

I had mud daubers block the pitot system in an aircraft that I flew once too.  Not fun!

The first thought is possibly that a build-up of dirt/bugs on the surfaces of the aircraft would affect the smooth flow of air and thus affect the amount of drag produced. This could, albeit quite slight, affect the flight characteristics of the aircraft.
There is a secondary thought, certain substances - especially bird poo - are quite corrosive and could therefore lead to more structural damage which is extremely hard to spot. You should keep your car clean for much the same reason - however on a car the worst you're going to get is a little rust spot on your bodywork. In the wrong place on a aircraft that could be a corroded rivet or bolt.

The amount of corrosion caused by bird poo is negligible... Especially to aircraft grade rivets and bolts, even over time. However a corroded spot on the "body" of an aircraft can cause a lot of damage, imagine a hole ripping out of your aircraft in mid flight, causing an exponential amount of structural damage. I.e. death.

@Jhawins I would not agree. Invisible corrosion on rivets can be substantial and is extremely dangerous, while laminating corrosion is rather good-natured, esp. with respect to detection and treatment.

@yankeekilo you raise a good point. I will have a question related to this later on.. After all, every question helps the beta site.

@Jhawins absolutely. I have no data on bird poo, but is rather alkaline stuff.

A rough surface on the leading edge of the wing has a surprisingly large effect. I tried to answer a similar/related question on the Skeptics site:
Can a sandpaper-thick layer of ice reduce lift by 30 percent and increase drag up to 40 percent?

The worst thing is a perfect flat surface, as you get a bond of static air to the surface. The flowing air has to pull away from this.
The best I have seen is when the wing surface has millions of small features which make the air turbulent - this is all on a macro scale at the surface.
The above flowing air rides over the turbulent air more freely.
Like a stack of steel plate on thousands of ball bearings. Imagine taking the bearings away and trying to slide the steel across the floor!
Sharks do this, their skin has details which stop the flowing water sticking.
Another way is the repel the air molecules at atomic level from the wing surface - reduces sticking.   You use a high voltage electrode on leading edge to charge the air
So the wing and the air now share like charges and repel each other - less sticking.
Thx for the opportunity to share odd memories of random facts from decades ago.
I have ran out of skill now and will probably not bother you again,, Steve

I know that the Supermarine company painstakingly blind riveted the leading edge of the spitfire wing as it proved faster.
They did a series of experiments some involving gluing split peas in rows to mimic domed rivets!


text:
Has anyone successfully solo'd a helicopter with no actual flight experience?
Especially at low speed, such as during takeoff, while hovering, and while landing, helicopters are famously difficult (impossible) to control for someone with no experience. Is there a documented instance of any person ever successfully taking off, hovering, and landing a helicopter with no actual flight experience? It must all be in one flight, first time--someone teaching themselves over multiple short flights / hours does not count.  Simulator use is OK and does not count as actual flight experience for the purposes of this question.

What about the first person to ever fly a helicopter?

Those guys went step by step over multiple flights. I'm looking for someone who went up for more than just a few seconds on their first ever flight, remained in control, and landed.

I very much doubt it. This guy tried and failed

I've never flown a helicopter, but I think if it as being like operating a motorcycle, where each limb has specific combinations of things to do in order for smooth operation.

By 'flight experience' do you mean 'helicopter flight experience'?

Yes, I mean helicopter flight experience.

Yes, Eric "Winkle" Brown took delivery of a Sikorsky R-4 and flew it after reading the flight manual and getting a briefing from a USAF Sergeant. He had no experience or training in helicopters. He wrote about it in "Wings of the Weird and Wonderful".

His story on the linked wikipedia page is outstanding -- well worth the few minutes to read it for anybody with an interest in aviation history from the 1930's-40's-50's era.

While having no helicopter flying experience, Brown was an experienced fixed wing pilot.

Brown made several practice attempts before his flight. Great example of a self-taught heli pilot, but doesn't count.


text:
Are lockwires still preferred over self-locking nuts and other ways of bolted joints` safety?
I've watched some of the lockwiring videos and if I understood it right then there are two most widely used ways of ensuring that a bolted joint does not get loose:

Lockwire
Self-locking nuts

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:
Do they now use other methods of bolted joints` safety in gas turbine engines (jam nuts and locking washers in particular)?

Are you asking exclusively about turbine engines, or about aircraft in general? Also, are you asking about new designs, or about latest maintenance practice on equipment of any vintage?

@JonathanWalters My curiosity is not limited :) The more information on the topic i.e. "bolted joint safety in aviation" the better. Not historical information but the current trends, achievements and standards.

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:
Do they now use other methods of bolted joints` safety in gas turbine engines (jam nuts and locking washers in particular)?

Well, maintaining safety lockwire isn't as hard as you think it is: A pair of safety wire pliers will last you a lifetime, and they do about 80% of the work for you (all the maintenance monkey needs to do is cut an appropriate length of wire, hook up the pliers, and twist, making sure the wire is positioned so as to always tighten the fastener).
It is easy to inspect, repairing is simple (just replace the damaged wire), and cost for a spool of wire is minimal compared to using a new self-locking nut every time something needs to be taken apart (safety wire earns its keep for temporary assembly too: You can wire the assembly when you're done, rather than wearing the lock material on a self-locking nut).
Other methods of securing fasteners are used on aircraft (in engines and elsewhere), including cotter pins and self-locking nuts with nylon inserts to prevent them from slipping. The cotter pin is easy to verify (like safety wire), and is widely used.  Self locking nuts on the other hand can slip without much visual indication (torque seal or similar products are often used to mark the nut and fastener to give a visual indication of slip).
A disadvantage to self locking nuts is that they must be replaced any time the fastener is removed (reused nuts will have a lower locking resistance, and may fail to hold), and using them introduces a potential for human error in maintenance operations that does not exist with safety wire, which must be cut to remove it. (There are even folks who try to reuse cotter pins, though normally they are cut to remove them and thus cannot be reused.)

Hi. Thank you for the information. Is my reading of your answer as: "No, lockwire and self-locking nuts are still the main ways to provide bolted joint reliability in aviation in 2016" correct?

Do you have a reference for a requirement to replace self locking nuts after every removal? That is not necessarily industry practice and I am not aware of such a requirement. There are lots of cases where non-critical components, such as engine baffling, are secured with self locking nuts.

@JonathanWalters Recommendations vary on reuse: I know the air force requires self-locking nuts in "critical areas" to be replaced every time they're undone, but I believe they allow reuse in non-critical areas (cosmetic attachments, etc.). FAA AC43.13-1B allows reuse of self-locking nuts if the running torque is within a specified limit range, and if it's lower than that the nut must be replaced as the insert is too worn to provide security. At my (non-aerospace) job we have bags of nylock nuts & just replace them each time though: We're lazy and thats easier.

@voretaq7 Ok, those are the advisories I had in mind. We typically reuse nuts in non-critical locations, but replace in locations such as control surface applications. A lot of aircraft applications also use fully metal self locking nuts, especially in engine applications, and these seem to wear less than nylock nuts.

Lock wires are the most basic of maintenance. I being a maintenance person use lock wire every where and every nuts and bolts possible.
I haven't analyzed the financial part of using it but I would say it is the most safest means of securing because it cannot be loosened unless you cut the wire but self locking nuts are sometime found defective. Other means such as securing with tap washer or spring washer are also less effective compared to lockwires as the tap washers can slip sometimes and you may not have noticed it. Hence, unless it is impossible to use lockwire or its very difficult at the moments; It is always recommended to use lock wire wherever possible.

Do you work with the relatively modern engines or the older ones? Your answer is clear but what is your field?

I am currently working with LET 410 UVP- E20 Turboprop aircraft, I am in the engineering department; maintenance guy basically.
And as far as I know even the Airbus Aircraft extensively use lock wires. For, the connecting hoses there isn't going to be an alternative for lock wires.


text:
Which aircraft is a single-prop, low-wing aircraft with prominent rivets and three canopy windows?
We would appreciate help identifying an aircraft that my daughter saw. It is a single-prop, low-wing design with a round fuselage and very prominent rivets.
It had a prominent canopy that stood above the fuselage with visible windows, and the rudder was visibly slated as well.

The very mention of 'prominent rivets' makes me immediately think of Douglas aircraft, such as the SBD Dauntless.

Why the downvotes? There are many aircraft identification question on this site, the question is even tagged for it!

Can you tell us where you saw it? And does your daughter remember anything about the color or markings?

@Pondlife She just sent to me the drawing. I don't know if she saw it on the ground or in the air. I'll ask tomorrow when I see her if we don't have a good candidate by then. Thanks!

This seems hopeless. The detail level of the drawing is just "OK, it's a low-winged single-seat prop plane with rivetted construction." It could be anything.

@DavidRicherby: You underestimate the Aviation.SE community as a resource. Mike Sowsun answered the question perfectly below!

When I saw your daughter’s drawing I thought of the Vultee P-66 “Vanguard”.

But the Republic P-47 “Thunderbolt” might also be a good candidate.

Thank you! I'll show her this post and we'll answer together.

P-47 it was. She saw a drawing of one in class. Thank you!

I am amazed at this result :D


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What is the purpose of the extremely high cabin altitudes in military aircraft?
The Lockheed SR-71 and the (old) Lockheed U-2 were engineered to maintain cabin altitudes in excess of 25000 feet AMSL at an altitude of more than 70000 feet AMSL.
However, in both airplanes, pilots are required to wear space suits which maintain the safe pressurisation and oxygen content anyway. If the space suit develops a pressurisation leak, I think it's unlikely that the very high cabin altitude in these airplanes would buy the pilots any more time to descent to a safe altitude safely as the time of useful consciousness at 25000 feet AMSL is the order of a few minutes. Furthermore, it seems strange that aerospace engineers would install a pressurisation system on the Lockheed U2, an airplane already struggling to be as light as possible.
So why is this pressurisation maintained at such a high altitude in the airplanes?

Even the unmanned RQ-4 Global Hawk has a pressurized compartment. The low air density at altitude would not be sufficient to cool the electronics, so a pressurized electronics compartment had to be added.
I am not sure, but I expect the same reason required pressurization in the U-2 and the SR-71. The electronics were, besides the pilots, also an occupant of their pressurized cockpits.
At the pressure of 25.000 ft a human will not stay conscious, but will be able to survive. When the pressure drops below that of 30.000 ft, the breathing reflex will stop. If the pilot initiates a descent when his pressure suit starts to leak, he has a good chance of waking up at lower altitude before the aircraft hits the ground if the cabin can prevent the air pressure from falling to that of ambient air.

Wikipedia suggests that some pressurization was needed so that an aircon system could cool the cockpit.

@DavidRicherby: So pressurization was needed to cool all cockpit occupants, humans and electronics.

Isn't it very cold anyway at FL700+?

^at least in the U2's case I mean.

Regardless of the temperature, with insufficient air pressure convective heat transfer just doesn't work.  It can be mighty cold in space (if in the shade), but it's non-trivial to get rid of that heat (you have to resort to radiative cooling, far harder).


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What are good books to learn basic aerodynamics in plane design?
Well, since this stack is in beta, I thought I'd take a wack at asking a book question to see how it fits in this particular community (of if it even fits to begin with).
I'm very curious about how aerodynamics work in plane design (especially wing design), but it's hard for me to ask questions here because I'm lack knowledge of so many of the basics.  So I wondered if I could get a recommendation on a good book to learn the basics of aerodynamics?  Keeping in mind that my understanding of math is limited, so I would need a book that explains the math being used to some extent.
Bear in mind when answering:  This is a Q&A site, so try and have some reasoning behind why your book is the best.  Especially if you could show it has good explanations of the math and, also, the books is good for the somewhat beginner.
Let's see if this works...

Book recommendations are generally not good fit for this Q&A format, but as you say lets see how the rest of the community respond

@Jamiec. Basically.  I kind of wish that SE had a special area for book recommendations, as I think it would be awful useful.  There's just a lot of smart people here, so I'd like to know their recommendations.

I neither agree nor disagree, but its certainly something relevant to the wider community. Make the suggestion: http://meta.stackexchange.com/

@Jamiec: is already there

Theres a stack of books for aerodynamics here -- https://www.goodreads.com/shelf/show/aerodynamics

I've converted this to a Wiki so if the community decides it gets to stay it can have one authoritative answer ala The C++ question. (The side effect is "Sorry guys, no rep" :-/ )

@voretaq7 I'm not personally concerned, it's what I wanted in the first place :)

Beginner

Fundamentals of Aerodynamics by John D. Anderson, Jr.
Introduces the basics of aerodynamics with historical background, the mathematical explanation and some practical applications. In the latest edition,  Computational Fluid Dynamics is also discussed.
Mechanics Of Flight by Warren F. Phillips.
Anderson's book is a good text for understanding the building blocks of fluid dynamics, such as the different types of flow. It is good for understanding how airfoils and wings work, as well as understanding the microscopic flow considerations. Phillips' text also talks plenty about flight dynamics and control, so you can better picture the forces acting on an airplane.
Anderson's and Phillips' make a very good learning pack.

Intermediate
No books found as of yet
Advanced

Fluid Dynamic Lift & Fluid Dynamic Drag both by Hoerner
I wouldn't consider these to be great "learning" textbooks, and the math can get very intensive at times, but these are still go-to reference text, and they are a great resource if you want to start a "deep dive" into aerodynamics and the practical effects of various design decisions. Both books are replete with wind-tunnel testing information and diagrams, as well as the supporting equations to back it all up.

Classics / Older

Aerodynamics for Naval Aviators by H. H. Hurt Jr.
This is a good primer on basic aerodynamics - as the title implies it's primarily aimed at naval aviators, but the material is pretty accessible and much of it is applicable to all fixed-wing aviation. There's even some helicopter stuff in there, though the section is rather thin.
This book is available from a number of publishers. It is also known as NAVAIR 00-80T-80 or NAVWEPS 00-80T-80 and available from the FAA in PDF form.

Additional references
As far as mathematics goes, you can get Stewart's Calculus text. It is a pretty good book with quite satisfactory explanations, and you can get an older edition for almost nothing (make sure you get the full text with both single variable calculus and multivariable calculus sections). Without a basic understanding of calculus it will be difficult for you to get a good grasp of the aerodynamics material.

I'm with DeltaLima's book recommendation [pdf].
Otherwise, this chapter of a larger ebook covers some basic aerodynamics: http://www.av8n.com/how/htm/airfoils.html

I'm thinking we should keep this answer around as "the web pages list" -- not necessarily textbooks, but web pages with good explanations?

I don't know a book which will provide you with a thorough mathematical explanation and at the same time treat the aerodynamic content in depth. Perhaps one exists, but I have not come across it as yet. I would recommend that you you can go for a book like Fundamentals of Aerodynamics by John D. Anderson, Jr., and simultaneously refer to a mathematics book which will give you the necessary background knowledge. There are plenty of books which can serve this purpose.
Anderson's book, meanwhile, presents the material in a manner which is quite easy to understand, and build a strong foundation of aerodynamics and its applications.
However, if you feel reading a mathematics book might take away a significant quantity of your time, another book I would recommend is Flight Without Formulae by A.C.Kermode. It is a classic book on aeronautical engineering, and covers the various aerodynamic phenomena over a wing. In my view, it is quite apt for a beginner.

A famous reference is: 'Aerodynamics, selected topics on the light of their historical development', by Theodore von Karman. There's also a site: Desktop.Aero offering a digital textbook on applied aerodynamics, but as I'm not engineer, I never went beyond cover page. NASA/NACA Cranfield database contain lots of aviation related papers since very early, a link to a list exists in Rotaryeng.net site: NACA UK Archive results page

Nobody mentioned the FAA handbooks yet, so I will. The FAA has a cornucopia of handbooks on various aviation-related topics, and in particular has a few on aerodynamics. They have the advantage of being easy to find, written to be understandable by anyone, and available free of charge. Here are a few
In particular, I would recommend reading aerodynamics of flight. It was written for student private pilots, so everything discussed pertains to aviation, and it does not assume that the reader has more that a high school education.
There are other books, that are aimed at the same public, but that expose the aerodynamics of helicopters or of gliders, though the contents of these books partially overlap, of course.
Finally, this manual is a bit outdated, but the first section features a useful glossary of aero terms.


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What are the drawbacks of being a helicopter and fixed-wing pilot at the same time?
Are there any drawbacks if someone who is a fixed-wing pilot, learns to fly a helicopter, or vice-versa? Specifically, are there instinct actions in one category that are dangerous in the other?
Does this differ if someone is experienced in one category (e.g. 1000+ hours), versus a student learning both within a short period of time (e.g. less than 6 months in between)?

I imagine it's hard to use both sets of controls simultaneously. Also, you're physically straddling an airborne aircraft and an airborne helicopter.

Cost seems like a major drawback :-)

My experience transitioning from airplanes to helicopters and then to gliders is that I never forget what I'm flying.
I know that sounds obvious, but its no different than the difference between driving a car with automatic transmission and manual, riding a motorcycle which has all the controls in a different place than a car and countersteers, and flying an airplane.
I don't reach for the throttle when I want to slow down in a car, and I don't turn the wheel in the direction of the turn when I'm riding a motorcycle. Similarly, when taking off in an airplane, I know I have to add power and pull back a bit to get it off the ground, and in a helicopter I inch the nose forward to gain ETL.
The reason I don't act/react improperly when flying different aircraft is that it's all been trained into my muscle memory to do the right thing depending on the circumstances. I don't think of the horn in a helicopter as a stall horn, just like the buzzer in my alarm clock and smoke alarm are not stall horns. The horn in the heli is a low-rpm horn, and I ease the stick back not forward.
Another complication is instrument flight. Although I am an instrument rated airplane pilot, I have a little hood time in a helicopter.  I'm so used to flying pitch and power against the AI that all my instincts under the hood in the heli were completely wrong. Nevertheless, I don't think I'll ultimately have any trouble flying instruments well in a heli.

You've never stepped on a clutch that wasn't there in an automatic car? I guess that's one good reason I'm not a pilot.

I've felt the urge to pull back on the steering wheel in
a car sometimes to slow down when braking (aerodynamic braking in a plane on the runway)...

In case of an engine failure, the fixed wing pilots natural reaction is to push forward to lower the nose, then look for the correct glide airspeed. A helicopter pilot in most engine failures should pull back (although not agressively) to load the disc and restore, or increase rotor RPM.  Maintaining rotor RPM is the only way to get to the ground safely so flaring is an instinctive reaction trained in.  You don't look for airspeed or rotor RPM.  You dump the collective and flare, then have a look at airspeed and RPM.  Pushing forward will reduce rotor RPM which in some flight phases and some helicopters might not kill you but in many helicopters at altitude may well kill you.  In addition, a stall buzzer will prompt the fixed wing pilot to push the stick forward and increase power, which in a helicopter means pulling the collective.  In a helicopter the low rotor RPM buzzer sounds just like a stall warning but pushing the stick forward and pulling the collective will almost certainly kill you.
Another action that has to be instinctive is to stick in a boot full of right pedal (counter clockwise rotor) which is totally alien to a single engine fixed wing pilot in an engine failure and completely the opposite of what a twin engined fixed wing pilot might do, who will naturally "step on the failed engine".  In a helicopter, that can get you into a very bad attitude rapidly from which it might be impossible to recover.
Negative G in an aircraft is not a problem. In a 2 bladed helicopter, you must gently pull back to reload the disc.  Pushing forward has a real risk of a blade chopping off the tail or hitting the canopy. It might also cause "mast bumping" which can cause the rotor to separate from the aircraft.  Too many helicopter pilots have been killed this way. Most helicopter pilots avoid -ve G.  The main point here is that you do not push the stick forward to level out from a climb.  The instinctive reaction for a helicopter pilot is to to pullback as soon as they feel the slightest hint of rising out of their seat.
In a helicopter, to accelerate, you push the stick forward then increase power to maintain altitude or climb.  In an aircraft, you increase power, then push the stick forward to maintain altitude.
A running landing, and not a hover landing, requires you to push the stick forward to level the skids.  A fixed wing tricycle gear pilot wants to pull the stick back to flare which again, might chop off the tail.
Keeping trim (balance) is a function of power and not direction of turn.  It is perfectly possible to make a properly executed balanced turn in a helicopter with the opposite pedal pushed in.
Helicopters can slow down with a nose down attitude and you take off by pushing the stick forward to accelerate.
I'm sure there are others which I've forgotten but I think these are the main things and, most importantly, as I've shown, trying to fly a helicopter like a fixed wing can be deadly.
In summary, flying helicopters is very different to flying fixed wing and you need different responses which need to be intuitive, especially in emergencies.
My gut reaction response is that it is easier to transition from helicopter to fixed wing and that the lower time pilots will find it easier because the years of experience and muscle memory are not there.

"boot full of left pedal" I don't agree. there are CW and CCW rotor systems, and either engine can fail on a multi. people can and do learn to do the right thing.

negative Gs are only a problem with 2-bladed systems, like robbies and bell 206.

wheel landings in an taildragger require you to push the stick forward on landing, not back

re: coordinated turns. in mid to steep turns in airplanes, overbanking tendency requires stick opposite the turn and rudder into the turn. i just fly by keeping the yaw string centered, no matter what aircraft/regime

sorry for the flurry of comments, but I wanted to make each one discrete. for the record, I am rated for airplanes, gliders, and helis.

"boot full of left pedal", I did put in brackets (CCW rotor) but also mistakenly said left pedal, now fixed.   Negative G for 2 blades only, agreed.  Agreed on keeping the string centred.  The point is, I have seen on here a few times that helicopters are just liked fixed wings.  I hope that I have done enough to demonstrate why that is not so.

have you flown high-performance airplanes? anything with 200 or more horsepower needs rudder trim or a yaw damper, and in the case of engine failure at cruise or full power, you'll need your feet hard on the pedals to keep the plane in trim as you pitch for Vglide. I really think the entire 'graph  needs to go.

I agree completely that there are too many "fixed wing" answers to helicopter questions, and your answer does a great job of pointing out the diffs. I would also say that there are too many "fixed-wing" votes on "fixed-wing" answers, which is even more unfortunate.

I would really like to upvote this answer, but there are still just too many unaddressed issues, even after your edits

I don't know how to improve it!  I can't see any factual errors, so the only things I could do would be to add "except in a high performance single engine aircraft" or "except in a taildragger" and so on.  I'd end up with 2000 words.  Any suggestions?  I also generally don't mind edits, although I did once have one answer edited from being correct to being wrong ;)


text:
Can you file a flight plan to an airport whose runway is NOTAMed closed?
We're planning a flight (under IFR) to an airport where the runway is notamed closed until 1900L.  The airport authority has said it will likely be open much earlier, so we're hoping to to take off and have the runway open by the time we arrive.
Is it acceptable under part 91 or 135 to file a flight plan to an airport whose runway is NOTAMed closed?
I can't find anything relevant in the FARs or the AIM.

I don't see why not, although you can't land there, so why would you? Are you talking VFR or IFR?

At least in the military world, you could file to a point in space, so I can't see why not.  Why do that? Get out of town IFR, fly to the point where you descend into your low-level route, cancel IFR, descend & fly the route, and then pick up a whole 'nuther flight plan at the exit point. In that world, it worked fine. For Part 91, it seems like you ought to be able to file to "the point in space formerly known as KXYZ". Maybe a place to fly practice GPS approaches, with little/no traffic conflicts?  For Part 135, that seems more iffy, but I wouldn't be shocked either way.

If you can tell us why you want to do that, it might help to get a better answer. And do you mean the airport is closed, or the runway is closed? I ask because some airports allow flight operations from taxiways or grass areas if the runway is closed.

Could the airport be NOTAMed closed at the time of filing, but with an effectiveness that ends before the ETA?

IFR.  Runway is notamed closed until 1900L(our ops don't allow landing on taxiways if there are other options and grass is no good for a jet).  Airport authority has said it will likely be open much earlier.  Wanting to take off and hopefully it will be open by the time we get there.

With the added info in the comment, I'm going to say that it should be okay.

IFR. Runway is notamed closed until 1900L(our ops don't allow landing on taxiways if there are other options and grass is no good for a jet). Airport authority has said it will likely be open much earlier. Wanting to take off and hopefully it will be open by the time we get there.

My reasoning is: you can file to airport (A) that has an instrument approach that will get you down below the weather (say a 3000' overcast), fly the approach until you're in VMC, cancel IFR, and proceed VFR to airport (B), which is where you actually intend to land (but which has no instrument approach to get you below the weather -- and no radar coverage).  This plan works even if airport (A) couldn't accommodate your aircraft for some reason -- runway closed/shortened, weight bearing capacity, whatever.  (Obviously you'd need alternate plans if the weather didn't cooperate with going VFR from A to B, but let's assume that you have a place to go land and plenty of gas to get there for a case like that.)  What matters is that you have an approach you can fly at Airport A, not that you can actually land there.
Worst case, perhaps you could file to airport A where you want to land, and then after that file routing to airport B which is where you'll go if the runway doesn't open up in time.  Thus your filed flightplan is simply "I'll fly an approach at A then go land at B" and that's a perfectly workable plan even with the NOTAM as written.  Then, in flight, if the runway opens early as expected, you tell ATC to amend your destination to airport A and you're all set.
Disclaimer, IANAL (I am not a lawyer), but this seems entirely workable to me.  I know in the 121 world, we explicitly ARE allowed to file to an airport below our mins, with the hope that it comes up (better than forecast) above mins by the time we get there.  It requires extra alternates and such, but just because we "won't" be able to land there based on things as we see them at this moment doesn't mean we can't be dispatched to go there.  And if things get better (weather comes up better than forecast, runway reopens sooner than NOTAM'd), you get to do what you'd hoped for all along.  Just have a sound plan for what you'll do in the scenario where things don't.

Does ATC have no problem with flying an approach to a different airport than you intend to land at? And should you inform them ahead of time that's what you are intending to do, maybe in comments on your plan?

I don't know about Part 135/121 ops, but for Part 91 much like in the military you can file a flight plan to a point in space if you so desire (pilots do this for private airfields without identifiers, and helicopter pilots sometimes do it because they can land pretty much anywhere they want so if their flight terminates in the middle of a park that's their destination).
As far as the flight plan system is concerned there is no issue here: It's just noting your point of departure, route, and intended point of landing.
It doesn't really care if you can't land there, only that you intend to.

You may encounter some pushback here from Flight Service if you file by telephone ("That airport's runway is NOTAM'd closed during your arrival time, are you sure you want to file this?"), and they'll certainly mention it to you if you call for a briefing.
ATC may also mention it to you while you're enroute, but ultimately checking the NOTAM and complying with the closure is your responsibility as a pilot.
Obviously it goes without saying you should have a suitable alternate airport planned in case the runway doesn't reopen early, but I'm sure you've already plugged that in to the "alternate airport" box on your flight plan.

authors: Сергей Борисов

authors: จตุรงค์ สุขสังข์


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How are aircraft transported to, and then placed, in an aircraft boneyard?
I was looking at the boneyard at Davis Monthan Air Force Base and was wondering:
How are aircraft brought there, and then how are they placed so tightly together?

Almost always a plane going to a boneyeard is flown to the general area. Typically they are taxied, towed or dragged away from the airport itself. CHEAP is the key word in any recycling / 2nd-hand operation. Planes at the end of their economic lives, that cannot be flown because of damage or lack of maintenance, tend to be moved out of sight, valuable bits and hazardous materials removed, and the hulk reduced to scrap using normal construction/demolition equipment. The scrappers near Mojave airport work the same way, in a bare dirt lot down the street from the storage adjacent to the airport.
I've been to AMARG*, at Davis-Monthan, to Mojave Airport/Spaceport and a facility for smaller, general aviation, aircraft, Cessna 150s through commuter and business turboprops/jets. The later had a large, grass, field, for last landings. Other planes arrived by truck, in pieces. Most airplane museums are near an airport, but exhibits are less likely to fly in.
A plane headed for a museum or restoration shop, even as a donor, is often disassembled and sent by truck, train or ship. But restoration isn't scrapping, the economics are different.
*AMARG, or the 309th Aerospace Maintenance and Regeneration Group (previously known as AMARC, the Aerospace Maintenance and Regeneration Center)

Most are just flown in to Davis-Monthan AFB and then towed over to the boneyard where they're 'pickled'.  There are a couple different levels of preservation depending on it's potential future (returnable to flight, parts, etc.).  More information is available at the AMARC web site.

Convenience is a driving reason many boneyards in the US (like Davis-Monthan, Roswell, and Goodyear) are collocated with airports.

The aircraft can be placed very tightly together when they're being towed -- far closer than would be safe if they were being taxied, and at least somewhat closer than would be normal for parking if the expectation was they they'd be towed/pushed back out in a day or three.  The desert there is big, but it isn't unlimited, so there's nothing to gain by wasting parking space with extra unnecessary feet of space between aircraft that probably will never move again.
And by the time that they're being towed to their final parking spot, they aren't in a condition to taxi under their own power anyway -- engines have been purged of all fuel & oil (if not removed outright), etc.